What is a SIM lock?
From EjWiki
SIM lock: A sim lock, network lock, carrier-lock, imei-lock or (Master) SUBSIDY lock is really a technical limitation built into CDMA and GSM mobile phones by manufacturers to be used by carrier networks to limit the use of these phones to specific countries and/or networks. This is contrary to a mobile phone (retrospectively called SIM-free or unlocked) that does not enforce any SIM restrictions.Unlocking a smartphone is virtually universally legal. Additionally, it's legal for service providers to force SIM locks for certain amounts of time, varying by location.
Unlocking Technology: Commonly, a locked mobile phone will show a message if a restricted SIM is used, requesting the unlock code. On new phone models working on Android os software, the mobile phone will display a message saying “SIM network unlock PIN” or “Enter Network Lock Control Key” if it's network locked. Windows phones will show the message, “This SIM card can only be used on specific networks. Contact your customer service center for the unlock code”. Some other models may very well show differing messages that include "Enter special code" or "Enter unlocking code," or in some circumstances the mobile will simply present a message stating that it is locked. As soon as a valid code is typed in, the mobile phone displays "Network unlocked” or “Network unlock successful”.
Economics: Device producers have financial incentives both to enhance SIM lock protection (which placates network companies and enables exclusivity deals) and weaken it (extending a phone's appeal to buyers that typically are not interested in the service provider that offers it). At the same time, making it very hard to unlock a mobile may make it considerably less attractive to mobile phone network service providers with a legal obligation to offer unlock codes for certain devices or in particular countries.
Unlocking Services: Lots of organizations offer a network mobile phone unlocking service. This service needs all those whom would like to unlock a handset to provide their IMEI number to a service supplier and often they will also request the country and network the mobile phone handset is locked to, either sent by email or entered on their web-site. The company will then provide (for a fee) the unlock code for the mobile phone handset.
Unlocking Service Providers: Disappointingly there are a large number of dodgy online retailers operating in the smart-phone unlocking industry. Consequently it is prudent to be sure you use a reputable service provider for this service. Do your due diligence and investigate every prospective retailers before choosing to making an order. In the case of on-line providers, make sure they document their official business name and matching registration information (all legitimate organization should be lawfully registered with the official authorities in their country of origin) and ensure they give a genuine listed address and contact information on their web site. Furthermore make sure that any payments made are done so thru legitimate methods such as a recognised bank or financial institution using a debt or credit card, but do not ever make payment via a direct transfer since this offers no fiancial security. To aid with your search for a reputable company, we've provided an inventory beneath (and in no specific order) of a number of legit organizations currently offering such services.
